User blog comment:Long Patrol Girl/Photoshop Help, Please!/@comment-986811-20100110031853

Hmmm, I found this interesting tutorial on the Internet about Photoshop, one of the things I followed there to get rid of haloes was: Go to Image-Adjust-Levels, or hit Ctrl+L. A small window will open up, then you move the black triangle to the right to make your lineart nice and black, and then move the white triangle to the left until the paper area is white.

Hope this helps, it worked for me!